MgAl₂O₄ single-crystal fiber Bragg gratings for ultra-high temperature sensing

This work demonstrates third-order fiber Bragg gratings (FBGs) inscribed in MgAl₂O₄ single-crystal fiber (MSCF) using the femtosecond laser line-by-line (LbL) scanning technique. The MSCF Bragg gratings (MSCFBGs) show excellent stability and repeatability from room temperature to 1800°C, with a maximum temperature sensitivity of 39.74 pm/°C. Strain sensitivity increases with temperature, reaching 1.72 pm/με at 1600°C. Multiple high-temperature cycling experiments confirm that the gratings can operate stably at 1800°C. Furthermore, a cascaded array of five gratings is fabricated in an MSCF, demonstrating good wavelength-division multiplexing capability and quasi-distributed sensing potential. This study provides a promising technical solution for high-temperature monitoring in extreme environments.